Florence has re-intensified into a hurricane, and is expected to rapidly intensify into a very dangerous Category 4 hurricane by Tuesday as it heads towards the Southeast U.S. Coast. Florence is likely to make landfall on Thursday evening or Friday morning on the Southeast U.S. East Coast, or remain just offshore. The odds have increased that Florence will stall on Friday and meander near or over the coast for several days, making the hurricane a huge rainfall and coastal flooding threat.

Florence was about 750 miles southeast of Bermuda late Sunday morning, moving west at 6 mph. Sea surface temperatures (SSTs) were a warm 28.5°C (83°F), but Florence was embedded in an atmosphere with somewhat dry air (a mid-level relative humidity of 50%). The high wind shear of 20 – 25 knots that had been driving this dry air into the core of the storm had abated significantly on Sunday morning, and was a light 5 – 10 knots. Satellite images on Sunday afternoon showed that the storm was significantly more organized, with a prominent eye, a more symmetrical shape, and impressive spiral banding. Florence was a medium-sized hurricane, with tropical storm-force winds that extended out up to 115 miles from the center. A NOAA hurricane hunter aircraft flying out of Bermuda on Sunday morning found 75 mph surface winds. No other hurricane hunter missions are scheduled for today; regular hurricane hunter missions by the Air Force will begin on Monday. The NOAA jet will fly another dropsonde mission on Sunday night.

Intensity forecast for Florence: expect a Cat 4 by Tuesday

Florence’s environment has grown much more conducive for intensification, so much so that over the past day, NHC has made their most aggressive rapid intensification forecasts since at least 1998 for an Atlantic storm, according to an analysis by Sam Lillo. The SHIPS model predicts shear will remain low through Wednesday night. SSTs will gradually increase to 29°C (84°F) during this period, and ocean heat content will more than double, from 20 to nearly 50 kilojoules per square centimeter. Our top intensity models unanimously predict strengthening of Florence into a Category 3 or 4 hurricane by Tuesday, and the storm is also expected to increase in size. Florence will still be embedded in a relatively dry atmosphere, so it is possible the storm could suffer from dry air intrusions that would interfere with the intensification process, but this will likely not occur while the wind shear is light.